Pneumatically powered tools are used widely for forming dimples in workpieces, such as drywall panels, and for driving drywall nails or other elongate fasteners through such workpieces where formed with such dimples, into wooden studs or other substrates. Such tools are exemplified in Golsch U.S. Pat. No. 3,774,293 and Fishback U.S. Pat. No. 4,778,094.
Typically, such a tool employs a driving mechanism including a piston and a driving blade and having a high mass, along with a dimpler having a high mass and being shaped to form a dimple in the workpiece when struck by the driving mechanism. The dimple is a shallow recess, into which a nail is driven so that its head is countersunk. The dimple can be then filled with drywall finishing material, which conceals the nail head.
As exemplified in the patents noted above, it has been usual to arrange the driving mechanism and the dimpler so that the driving mechanism strikes the dimpler at a considerable distance from the workpiece.
In such a tool, as known heretofore, it is difficult accurately to control the depth of penetration of the dimpler into the workpiece because of the impact between the driving mechanism and the dimpler. The impulse of the impact therebetween can be calculated as ##EQU1## where V is the initial velocity of the driving mechanism before impact, m.sub.1 is the mass of the driver mechanism, and m.sub.2 is the mass of the dimpler.
Desirably, since it is difficult to reduce the mass of the driving mechanism, the mass of the dimpler should be low so as to reduce the impulse of the impact between the driving mechanism and the dimpler.